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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.searchlib.aggregation.hll;
/**
* This class is responsible for merging any combinations of two {@link Sketch} instances.
*/
public class SketchMerger {
/**
* Merges one of the two sketches into the other. The merge operation is performed in-place is possible.
*
* @param left Either a {@link NormalSketch} or {@link SparseSketch}.
* @param right Either a {@link NormalSketch} or {@link SparseSketch}.
* @return The merged sketch. Is either first parameter, the other parameter or a new instance.
*/
public Sketch<?> merge(Sketch<?> left, Sketch<?> right) {
if (left instanceof NormalSketch && right instanceof NormalSketch) {
return mergeNormalWithNormal(asNormal(left), asNormal(right));
} else if (left instanceof NormalSketch && right instanceof SparseSketch) {
return mergeNormalWithSparse(asNormal(left), asSparse(right));
} else if (left instanceof SparseSketch && right instanceof NormalSketch) {
return mergeNormalWithSparse(asNormal(right), asSparse(left));
} else if (left instanceof SparseSketch && right instanceof SparseSketch) {
return mergeSparseWithSparse(asSparse(left), asSparse(right));
} else {
throw new IllegalArgumentException(
String.format("Invalid sketch types: left=%s, right=%s", right.getClass(), left.getClass()));
}
}
private Sketch<?> mergeSparseWithSparse(SparseSketch dest, SparseSketch other) {
dest.merge(other);
if (dest.size() > HyperLogLog.SPARSE_SKETCH_CONVERSION_THRESHOLD) {
NormalSketch newSketch = new NormalSketch();
newSketch.aggregate(dest.data());
return newSketch;
}
return dest;
}
private NormalSketch mergeNormalWithNormal(NormalSketch dest, NormalSketch other) {
dest.merge(other);
return dest;
}
private NormalSketch mergeNormalWithSparse(NormalSketch dest, SparseSketch other) {
NormalSketch newSketch = new NormalSketch();
newSketch.aggregate(other.data());
dest.merge(newSketch);
return dest;
}
private static NormalSketch asNormal(Sketch<?> sketch) {
return (NormalSketch) sketch;
}
private static SparseSketch asSparse(Sketch<?> sketch) {
return (SparseSketch) sketch;
}
}
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